Anti-theft self-alarming tags, which have been widely known in the store security field, include micro-processor like micro-computer, abnormality state detection circuit and buzzer alarm circuit etc inside the tag. In an emergency, tag emits the alarm sound which makes people feel uncomfortable, and makes people know the occurrence of abnormality state.
Abnormality state which emits the alarm sound, defines such a state as the said self-alarming tag is removed from the merchandise and/or as the self-alarming tag receives the signal from transmission antenna of EAS (Electro-Article Surveillance) antenna which is installed at the store entrance.
As its alarm sound, the intermittent type alarm sound whose alarm sound frequency is several kHz and alarm sound repetition cycle is few cycle/second, or the swept frequency type alarm sound whose alarm sound frequency is swept during some definite swept frequency period between upper limit frequency and lower limit frequency, is used.
Both alarm sounds have the same characteristics that some specific frequency component appears at the definite time interval.
When tag emits the alarm sound at the store with background music or with noise sound or at the wide floor space store and with few store staff, sometimes its alarm sound is erroneously detected or it was difficult for store staff to identify the alarm position and/or the shoplifter.
In addition, when tag which emit its alarm sound, is destroyed and/or is put into the water pod, its alarm sound will disappear in a short time or it is also very difficult to detect this alarm.
Furthermore when centralized security is needed, in which store security information is controlled at the store security room, alarm information which specifies the alarm sound occurrence position should be input to the security server PC and alarm sound detection equipment which specify the alarm sound occurrence position and communicate those information to the security server PC should be needed.
In the related art, in order to detect alarm sound, electro-magnetic signal from the tag, which is emitted when tag emits the alarm sound, was detected. This electro-magnetic signal may be derived as its leakage flux from inductor used in the alarm sound driving circuit.
As the detecting method of this electro-magnetic signal, receiving antenna is generally used, which is incorporated into the EAS (Electro-Article Surveillance) antenna and this type antenna is mentioned as the related art.
But this type of antenna was rather big as 1 m H*40 cm W and its price also rather expensive. So it was difficult to place the receiving antennas at several places in the store and increase the security level.
And EAS (Electro-Article Surveillance) antenna has its weak points in which signal detecting sensitivity becomes lower in the following cases.
In some cases, EAS antenna may receive the power line noise from antenna-nearby electronic lamp or electric motor, or in some cases, EAS antenna may receive the effect of comparably big transmission signal to make the tag alarm.
In some cases, if this type of big antenna would be installed in the high end brand store entrance, the antenna existence, itself, might damage the esthetic entrance image, and so EAS antenna would be buried under the floor. And in this under-the-floor antenna case, the antenna would receive more nearby electro-magnetic noise from under-the-floor power line and its performance would become more instable and poor.
Usually, security equipment like anti-theft tag emits the alarm sound, and so the sound detection method which receives the sound through microphone and detects the alarm sound, may realize the small size detection equipment.
But by the store background music, customer's voice, outside noise and furthermore by the echo sound from such wall and/or ceiling as the construction object, the alarm sound may be affected and its alarm sound becomes fairly different from the original alarm sound and then reliable detection of the alarm sound seemed to be difficult and so far, sound detection method of the alarm was not used in the security field.
This invention can detect the alarm sound of anti-theft tag as sound and provide the reliable detection method of the alarm sound and furthermore can realize the small-size high-performance abnormality detection device which emits various security information for store security control and then integrated security system can be realized by the abnormal state detection unit of this invention.